According to the Or HaChaim HaKadosh, the Ruach HaKodesh that was given to the seventy elders was of the quality of the Ruach HaKodesh from Moshe Rabbeinu himself. It was from the "same level". However, that did not impact the level of the Ruach Hakodesh from Moshe Rabbeinu, his Ruach Hakodesh remained intact.
ויאצל מן הרוח, He took from the spirit, etc. The word ויאצל may have been intended as a clue to the source of this prophetic spirit, i.e. the עולם האצילות, a domain very close to the throne of G'd. מן הרוח אשר עליו, "from the spirit which was upon him;" this may describe the quality of that spirit. The source of the spirit which was bestowed on the elders emanated not from Moses but from higher regions. Alternatively, it may mean that after the spirit which imbued Moses was given to the elders, עליו, Moses' own spirit remained fully intact. Bamidbar Rabbah 15 states that when Moses evaluated the level of prophecy the elders attained, it turned out that the 2 elders Eldod and Medod (numbers 71 and 72 respectively) had received a higher degree of prophetic spirit because their portion came from G'd directly, whereas the other seventy elders received their prophetic spirit only from Moses. This was why the seventy elders prophesied only briefly.
According to the Rabbeinu Bahya, it was the Ruach Hakodesh from Moshe Rabbeinu that the seventy elders each received:
ויהי כנח עליהם הרוח, “it was when the spirit rested upon them, etc.” This refers to the spirit of Moses which they received. Concerning the Holy Spirit received by Eldad and Meidad the Torah writes ותנח עליהם הרוח (verse 26), meaning this spirit came directly from G’d.
Also the Malbim seems to explain that it was the Ruach HaKodesh of Moshe Rabbeinu that was "put" onto the seventy elders
So, it seems that "the Ruach Hakodesh from Moshe was given to the seventy elders" refers to the level and status of the Ruach Hakodesh that was given to the seventy elders. It resembled the level of the Ruach HaKodesh from Moshe Rabbeinu. It does not mean that it was taken from Moshe, but it was on the same lavel as Moshes'.